A conventional method of compressing the molding sand, which is fed in a molding space defined by a pattern plate and a flask placed on the pattern plate, by applying air to the sand, especially applying impulse pressure by compressed air, is known by JP Patent, A, 58-502090.
However, since the compressed air used in the conventional method is generated by an air compressor, a small amount of lubricant is contained in the air, and, when the used compressed air is discharged into the atmosphere, the lubricant in the air and tiny particles contained in the molding sand are also released together with the air. This tends to adversely affect the environment.
Further, it is known in a method that uses compressed air to form vent holes in deep pockets to enhance compaction (as taught, for example, by Japanese Patent, A, 55-120450).
However, forming a vent hole in a pattern increases the cost to make the pattern. Further, vent holes cannot be formed at any desired position because if one would be formed in a surface of the pattern that corresponds to a matching surface at which the mold and the molten metal contact, the surface of a product to be molded would bear the mark of the hole, thereby decreasing the quality of the product.
Further, when an impulse pressure by compressed air is used, the reflected impulse pressure causes cracks in the mold.
This invention is made in view of the above problems. The purpose of the invention is to provide a method to easily produce a mold without causing cracks therein and without forming any vent hole in the pattern, while at the same time making the environment clean.